Optical switches and tunable optical filters are valuable elements in modern photonic networks. For example, reconfigurable Wavelength Division Multiplexed (WDM) optical networks, including Metro networks, Passive Optical Networks (PON), and high performance computing, make use of different wavelengths for various purposes, including a form of addressing. As such, many optical/photonic networks need devices that allow the selection of a wavelength to be added to or dropped from the transport link. Optical switches and tunable filters are also valuable in instrumentation applications, such as spectroscopy. Accordingly, there is a need for tunable optical elements which can be used as components for such devices.
Optical switches that are low-cost, low-power, and of a compact size are important components in optical cross connects (OXC), reconfigurable optical add-drop multiplexers (ROADM), and other optical networking systems. Photonic Integrated Circuits (PIC), utilizing, for example, Silicon-on-insulator (SOI) technologies, can provide high speed and small footprint. Silicon-on-insulator (SOI) is a promising technology for developing optical switches due to its relatively large thermo-optic coefficient, high thermal conductivity and high contrast refractive index. In recent years, various thermo-optic switch configurations have been reported on the SOI platforms.
Microring resonators (MRRs), also known as Microrings, fabricated in photonic integrated circuits have been widely researched for various applications, including wavelength tunable filters for optical networks. A microring is a waveguide loop that is typically circular but in principle may be any geometry. The microring is optically coupled to one or two transport waveguides. In a scenario in which the microring is coupled to a single waveguide, it provides the ability to remove a set of wavelengths from the transport waveguide, thus acting as a notch filter. In a scenario in which the microring is coupled to two transport waveguides, the transport waveguides couple light to/from the microring. If light transported by the first waveguide includes wavelengths which are resonant to the ring, then the resonant wavelengths of light can be coupled from the first transport waveguide into the ring, and propagate around the ring to be coupled to the second transport waveguide. Wavelengths of light that are not resonant to the ring are passed from the input of the first transport waveguide to the output of the first transport waveguide, and do not substantially interact with the microring. Filters with desirable bandpass characteristics may be formed by coupling multiple microrings to each other with or without intervening transport waveguides.
However there is a demand for ever increasing speeds, and smaller footprints for such systems. Further there is a need to reduce optical loss of such components, especially as the number of MRRs within a PIC increase. Further it is known that polymer waveguides can also be used within PICs. A polymer waveguide has a three dimensional freeform fabrication. The transmission loss of polymer waveguide is smaller, but has a lower light mode confinement compared to higher refractive index material, such as Silicon. Accordingly, in order to support single mode light transmission, the minimum size of polymer waveguides is larger than that of silicon waveguides due to the lower refractive index contrast between the waveguide core and the cladding. Further, polymer optical waveguides cannot turn or bend as effectively as silicon optical waveguides. Accordingly, while polymer waveguides can be suitable as transmission waveguides, the extra size and larger turn radius makes MRRs formed from polymer waveguides impractical.
Accordingly, there is a need for a system and method that at least partially addresses one or more limitations of the prior art.
This background information is provided to reveal information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.